Radio receiver with reconfigurable baseband channel filter

ABSTRACT

A radio receiver circuit configured to receive a radio frequency signal and produce a baseband signal as an output therefrom has a channel filter having a bandwidth, the channel filter configured to receive the baseband output at a filter input and produce a filtered output at a filter output thereof. A signal-to-noise ratio (SNR) estimator prior to or after the channel filter or both is configured to estimate a signal-to-noise ratio of the baseband signal. A filter controller is configured to receive the signal-to-noise ratio estimate and control the channel filter to adjust the bandwidth thereof in accord with the signal-to-noise ratio estimate. This process thereby assists in improving SNR after the channel filtering by varying the channel filter bandwidth. This abstract is not to be considered limiting, since other embodiments may deviate from the features described in this abstract.

COPYRIGHT AND TRADEMARK NOTICE

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction of the patent document or thepatent disclosure, as it appears in the Patent and Trademark Officepatent file or records, but otherwise reserves all copyright rightswhatsoever. Trademarks are the property of their respective owners.

BACKGROUND

In radio receivers, often a baseband channel filter is utilized toseparate desirable signals that have been transmitted by a transmitterfrom undesirable signals (all of which are generally considered noise)that include adjacent channel signals, interference and noise. Thebandwidth of such channel filters is usually determined as a compromisebetween passing all of the desirable signals and rejecting unwantedsignal energy for a wide variety of changing real world applications.This compromise is seldom optimum and limits the quality ofcommunication.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the present disclosure will be described belowwith reference to the included drawings such that like referencenumerals refer to like elements and in which:

FIG. 1 depicts an example of a baseband spectrum overlaid with anassociated channel filter characteristics with overly narrow bandwidthin a high signal-to-noise ratio environment.

FIG. 2 depicts an example of a baseband spectrum with the associatedchannel filter's bandwidth characteristics optimized for the highsignal-to-noise ratio environment.

FIG. 3 depicts an example of a baseband spectrum and an associatedchannel filter characteristics having overly broad bandwidth in a lowsignal-to-noise ratio environment.

FIG. 4 depicts an example of a baseband spectrum the associated channelfilter's bandwidth characteristics optimized for the low signal-to-noiseratio.

FIG. 5 is an example of a block diagram of a direct conversion radioreceiver circuit implementation consistent with the present discussion.

FIG. 6 is an example flow chart depicting one implementation of achannel filter characteristic selection process in accord with thepresent discussion.

FIG. 7 is an example block diagram depicting the digital portion of aradio receiver consistent with certain implementations.

FIG. 8 is an example of a flow chart depicting a filter selectionprocess consistent with the present discussion.

FIG. 9 is another example of a flow chart depicting a filter selectionprocess consistent with the present discussion.

DETAILED DESCRIPTION

The various examples presented herein outline methods, and electronicdevices that estimate signal-to-noise ratio (SNR) in a radio receiverbaseband signal and use that estimate to optimize a channel filter'sbandwidth.

For simplicity and clarity of illustration, reference numerals may berepeated among the figures to indicate corresponding or analogouselements. Numerous details are set forth to provide an understanding ofthe embodiments described herein. The embodiments may be practicedwithout these details. In other instances, well-known methods,procedures, and components have not been described in detail to avoidobscuring the embodiments described. The description is not to beconsidered as limited to the scope of the embodiments described herein.

The terms “a” or “an”, as used herein, are defined as one or more thanone. The term “plurality”, as used herein, is defined as two or morethan two. The term “another”, as used herein, is defined as at least asecond or more. The terms “including” and/or “having”, as used herein,are defined as comprising (i.e., open language). The term “coupled”, asused herein, is defined as connected, although not necessarily directly,and not necessarily mechanically. The term “program” or “computerprogram” or “application” or similar terms, as used herein, is definedas a sequence of instructions designed for execution on a computersystem. A “program”, or “computer program”, may include a subroutine, afunction, a procedure, an object method, an object implementation, in anexecutable application, an applet, a servlet, a source code, an objectcode, a shared library/dynamic load library and/or other sequence ofinstructions designed for execution on a computer system. The term“processor”, “controller”, “CPU”, “Computer” and the like as used hereinencompasses both hard programmed, special purpose, general purpose andprogrammable devices and may encompass a plurality of such devices or asingle device in either a distributed or centralized configurationwithout limitation.

Reference throughout this document to “one embodiment”, “certainembodiments”, “an embodiment”, “an example”, “an implementation”, “anexample” or similar terms means that a particular feature, structure, orcharacteristic described in connection with the embodiment, example orimplementation is included in at least one embodiment, example orimplementation of the present invention. Thus, the appearances of suchphrases or in various places throughout this specification are notnecessarily all referring to the same embodiment, example orimplementation. Furthermore, the particular features, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments, examples or implementations without limitation.

The term “or” as used herein is to be interpreted as an inclusive ormeaning any one or any combination. Therefore, “A, B or C” means “any ofthe following: A; B; C; A and B; A and C; B and C; A, B and C”. Anexception to this definition will occur only when a combination ofelements, functions, steps or acts are in some way inherently mutuallyexclusive.

As noted above, in radio receivers, often a baseband channel filter isutilized to separate desirable signals that have been transmitted by atransmitter from undesirable signals that include adjacent channelsignals, interference and noise. The bandwidth of such channel filtersis usually determined as a compromise between passing all of thedesirable signals and rejecting unwanted signal energy for a widevariety of changing real world applications. This compromise is seldomoptimum and limits the quality of communication. These problems areameliorated in a system in which signal-to-noise ratio is estimated andthat estimate is used to control the bandwidth of a channel filter so asto enhance the signal-to-noise ratio out of the filter by eitherreducing the bandwidth to block frequency spectrum containing only noiseor increasing the bandwidth to capture a greater frequency spectrumcontaining useful signal.

Thus, in accordance with certain aspects of the present disclosure,there is provided a radio receiver circuit configured to receive a radiofrequency signal and produce a baseband signal as an output therefromhas a channel filter having a bandwidth, the channel filter configuredto receive the baseband output at a filter input and produce a filteredoutput at a filter output thereof. A signal-to-noise ratio (SNR)estimator prior to or after the channel filter or both is configured toestimate a signal-to-noise ratio of the baseband signal. A filtercontroller is configured to receive the signal-to-noise ratio estimateand control the channel filter to adjust the bandwidth thereof in accordwith the signal-to-noise ratio estimate. This process thereby assists inimproving SNR after the channel filtering by varying the channel filterbandwidth.

In certain implementations, the SNR estimator has a pre-filteringsignal-to-noise ratio estimator that estimates a pre-filteringsignal-to-noise ratio present at the channel filter input and apost-filtering signal-to-noise ratio estimator that estimates apost-filtering signal-to-noise ratio present at the channel filteroutput, and the filter controller is configured to receive thepre-filtering SNR estimate and the post-filtering SNR estimate andcontrol the channel filter to adjust the bandwidth thereof in accordwith the pre- and post-filtering signal-to-noise ratio estimate. Incertain implementations, the SNR estimator has a pre-filteringsignal-to-noise ratio estimator that estimates a pre-filteringsignal-to-noise ratio present at the channel filter input; and thefilter controller is configured to receive the pre-filtering SNRestimate and control the channel filter to adjust the bandwidth thereofin accord with the pre-filtering signal-to-noise ratio estimate.

In certain implementations, the SNR is estimated by calculating a FastFourier Transform (FFT) of a frequency spectrum present at the channelfilter input.

In certain implementations, the SNR estimator has a post-filteringsignal-to-noise ratio estimator that estimates a post-filteringsignal-to-noise ratio present at the channel filter output; and thefilter controller is configured to receive the post-filtering SNRestimate and control the channel filter to adjust the bandwidth thereofin accord with the post-filtering signal-to-noise ratio estimate.

In certain implementations, a demodulator is provided and the SNR of thebaseband signal is estimated at the channel filter output. In certainimplementations, the channel filter is realized as a digital filter withthe bandwidth of the channel filter selected by selection of a set ofchannel filter coefficients specified by the filter controller. Incertain implementations, the SNR estimate is mapped to the set ofchannel filter coefficients by the filter controller. In certainimplementations, the filter controller is configured to compare a firstSNR estimate at the output of the channel filter prior to adjusting thebandwidth of the channel filter with a second SNR estimate at the outputof the channel filter after adjusting the bandwidth of the channelfilter. If the second SNR estimate is improved over the first SNRestimate, then the adjusted channel filter is retained, and if thesecond SNR estimate degraded over the first SNR estimate, then thechannel filter is readjusted to have the pre-adjustment bandwidth. Incertain implementations, the baseband output comprises a baseband outputfrom a decimator. In certain implementations, the radio receiver circuitcomprises a direct conversion radio receiver.

A method consistent with certain implementations involves, at a radioreceiver circuit, receiving a radio frequency signal and producing abaseband signal as an output therefrom; at a channel filter having avariable bandwidth, receiving the baseband output at a filter input andproducing a filtered output at a filter output thereof; estimating asignal-to-noise ratio (SNR) of the baseband signal; and controlling thechannel filter bandwidth in accord with the estimate of the SNR of thebaseband signal.

In certain implementations, estimating the SNR involves estimating apre-filtering signal-to-noise ratio present at the channel filter input;estimating a post-filtering signal-to-noise ratio present at the channelfilter output; and the controlling involves receiving the pre-filteringSNR estimate and the post-filtering SNR estimate and adjusting thebandwidth of the channel filter therefrom.

In certain implementations, the SNR estimating involves estimating apre-filtering signal-to-noise ratio present at the channel filter input;and the pre-filtering SNR estimate is used to adjust of the bandwidth ofthe channel filter. In certain implementations, the SNR is estimated bycalculating a Fast Fourier Transform (FFT) of a frequency spectrumpresent at the channel filter input.

In certain implementations, the SNR estimating involves estimating apost-filtering signal-to-noise ratio present at the channel filteroutput; and the post-filtering SNR estimate is used to adjust of thebandwidth of the channel filter.

In certain implementations, the SNR is estimated at a demodulatorreceiving the channel filter output. In certain implementations, thechannel filter is implemented as a digital filter and selecting thebandwidth of the channel filter is carried out by selection of a set ofchannel filter coefficients to control the channel filter bandwidth. Incertain implementations, the filter controller is configured to comparea first SNR estimate at the output of the channel filter prior toadjusting the bandwidth of the channel filter with a second SNR estimateat the output of the channel filter after adjusting the bandwidth of thechannel filter. If the second SNR estimate is improved over the firstSNR estimate, then the adjusted channel filter is retained; and if thesecond SNR estimate degraded over the first SNR estimate, then thechannel filter is readjusted to have the pre-adjustment bandwidth.

In certain implementations, the SNR estimate is mapped to a set ofchannel filter coefficients. The baseband output is a decimated basebandoutput that is provided to the channel filter.

Another method consistent with certain implementations involves at aradio receiver circuit, receiving a radio frequency signal and producinga baseband signal as an output therefrom; at a digital channel filterhaving a variable bandwidth, receiving the baseband output at a filterinput and producing a filtered output at a filter output thereof;estimating a pre-filtering signal-to-noise ratio present at the channelfilter input; estimating a post-filtering signal-to-noise ratio presentat the channel filter output; and selecting a set of channel filtercoefficients for use by the channel filter that determine the channelfilter bandwidth in accord with the pre-filtering SNR estimate and thepost-filtering SNR estimate of the baseband signal. In certainimplementations, at least one of the SNR estimates is made bycalculating a Fast Fourier Transform (FFT) of a frequency spectrum.

A non-transitory computer readable storage medium consistent withcertain implementations stores information that when executed on one ormore programmed processors carry out a process involving receiving abaseband signal as an output from a radio receiver; filtering thebaseband signal at a channel filter having a variable bandwidth byreceiving the baseband output at a filter input and producing a filteredoutput at a filter output thereof; estimating a signal-to-noise ratio(SNR) of the baseband signal; and controlling the channel filterbandwidth in accord with the estimate of the SNR of the baseband signal.In certain implementations, estimating the SNR involves estimating apre-filtering signal-to-noise ratio present at the channel filter input;estimating a post-filtering signal-to-noise ratio present at the channelfilter output; and where the controlling involves receiving thepre-filtering SNR estimate and the post-filtering SNR estimate andadjusting of the bandwidth of the channel filter therefrom. In certainimplementations, at least one of the SNR estimates is made bycalculating a Fast Fourier Transform (FFT) of a frequency spectrum.

Turning now to the drawings, FIG. 1 depicts an example of a basebandspectrum 10 overlaying an idealized channel filter bandwidth 14 withoverly narrow bandwidth in a high signal-to-noise (SNR) ratioenvironment. In this illustration, the baseband signal has amplitudethat is much greater than the noise and interference level depicted as18. The useful frequency spectrum 10 exceeds the bandwidth of thechannel filter 14. This results in the channel filter being suboptimaland limiting the overall signal spectrum that can be used and thesignal-to-noise ratio that can be achieved in the radio receiver. Theportions of the radio spectrum (approximated by the dashed oval 20)lying outside the boundaries of the idealized filter bandwidth 14contain useful power that can either be used to improve error rate orthroughput. This filter would be more optimal for purposes of SNR if thebandwidth of the channel filter was wider.

FIG. 2 depicts an example of the same baseband spectrum 14 with theassociated channel filter's bandwidth optimized for the highsignal-to-noise ratio environment. In this case, the channel filterbandwidth 22 is made somewhat wider to take advantage of more of thepower present in the signal. The bandwidth 14 of the filter in FIG. 1,while narrower than that of the wider filter bandwidth 22 of FIG. 2,will be referred to as intermediate in bandwidth since it will befurther compared to an even narrower bandwidth later.

FIG. 3 depicts an example of a baseband spectrum 30 of a signal and anassociated channel filter having overly broad idealized bandwidth 34 ina low signal-to-noise ratio environment. In this example, the SNR ismuch lower than that depicted in FIGS. 1-2, and the channel filter withbandwidth 34 (same bandwidth as shown for 14) allows much more noise topass, as approximated by the dashed ovals 40. As a result, theunsuppressed noise shown in the areas of dashed ovals 40 representnearly pure noise resulting in a signal having suboptimal SNR to passthrough the channel filter. Virtually all of the signal in the regionsapproximated by dashed ovals 40 represent signal power that is unusabledue to the high noise.

FIG. 4 depicts an example of a baseband spectrum and the associatedchannel filter's bandwidth optimized for the low signal-to-noise ratio.In this example, the bandwidth 44 of the channel filter is reduced to anarrower bandwidth 44 as compared to the wider bandwidth 22 and theintermediate bandwidth 14 of FIG. 1 so that signal 30 is better isolatedfrom the noise thereby increasing the SNR of the signal passed by thechannel filter.

It can be seen from the above illustrations that communications undervarying communication environments can be coped with more effectively ifthe bandwidth of a receiver's channel filter can be adapted to theenvironment.

FIG. 5 is a block diagram of an example functional representation of aradio frequency (RF) receiver device 100. In this example, the radioreceiver device can be used, for example, for cellular telephone, pager,and data communications such as so-called “smartphones” and the like.This example is based on a homodyne or direct conversion radio which hasbecome popular recently due to reduced circuit complexity since aminimal numbers of mixers, filters and local oscillators are used. Suchdirect conversion radio circuits can often be realized using a highlyintegrated mixed (analog and digital) signal integrated circuit to carrymost of the components used in implementing the radio. Moreover, oncethe radio frequency signals are directly converted to baseband anddecimated, digital signal processing can be utilized for numerous radiofunctions.

In this example device 100, radio frequency signals are received at anantenna 104 and may be filtered by a filter (not shown) prior to orafter being amplified by a low noise radio frequency (RF) amplifier 108.This radio utilizes no intermediate frequency as with superheterodynereceivers, and so the output of the amplifier 108 is provided to a pairor mixers 112 and 116 without intermediate down-conversion. However,implementations consistent with the present teachings may also beutilized with other radio architectures including, for example,superheterodyne receivers and low intermediate frequency receiverswithout limitation. Mixers 112 and 116 are utilized to down-convert theRF signal from amplifier 108 directly to baseband and in the processcreate in-phase and quadrature signals (I and Q respectively). This isdone by mixing the output of an RF local oscillator 120 with the RFsignal at mixer 116 to produce the I signal. The Q signal is generatedby first shifting the phase of the output of local oscillator 120 by 90degrees at phase shifter 124 and then mixing the phase shifted versionof the local oscillator signal at mixer 112.

The I and Q signals are filtered at filters 128 and 132 respectivelybefore being passed to analog-to-digital converters (ADC) 136 and 140respectively. It is noted that the radio receiver 100 incorporates bothanalog and digital signal processing which may both be carried out in amixed signal integrated circuit or may be carried out in separate analogand digital circuitry. Generally speaking, the analog portion of thecircuitry appears in FIG. 1 to the left of ADC circuits 136 and 140 andthis leftmost portion of the radio is often considered the “analogradio” or “analog portion” of the radio, while the portion to the rightof the ADC circuits 136 and 140 are considered the “digital radio” or“digital portion” of the radio with the ADC circuits constituting thetransition point of the circuit from analog to digital. The conversionto digital signals creates digitized versions of the I and Q signals forsubsequent processing by a decimator 144. The decimator 144 providesanti-aliasing low pass filtering and down-sampling to produce a lowersampling rate digital signal that can be further processed in thereceiver.

The output of the decimator generally provides lower sampling rateversions of the I and Q signals that are provided as a decimatoroutput/channel filter input to be filtered by the channel filter 150. Inthis example implementation, the channel filter 150 is shown as avariable bandwidth low pass filter. In conventional radio receiverdevices, channel filter 150 has a fixed bandwidth. In this example, andin most example implementations consistent with embodiments of theinvention, the channel filter 150 is realized as a digital filter (e.g.,a finite impulse response (FIR) or infinite impulse response (IIR)digital filter). As shown, the filter processes I and Q signals and theI and Q signals are present through the detection process carried out atdemodulator 154. But, in other implementations, at any suitable point inthe processing the I and Q signals can be converted to a single endedsignal as dictated by the particular application. It is noted that thebaseband signal is filtered by the channel filter 150, and the channelfilter's output is also a baseband signal, albeit a filtered version ofthe original decimated I and Q values. The term baseband signal is usedgenerically herein to mean both or either filtered and unfilteredbaseband I and Q signals.

In accord with the present implementation example, the variable channelfilter is controlled by a channel filter control and decision logicblock 160. This block 160 in digital implementations controls thecharacteristics of the digital channel filter 150 by selection andinstallation of a set of filter coefficients used by the digital channelfilter 160. In certain implementations, the channel filter can berealized as, for example, a 24 stage finite impulse response (FIR)filter (i.e., a filter whose impulse response has a finite length), butthis is not to be considered limiting since other digital filterrealizations are also possible.

In an example FIR filter, the output of the filter is given by aweighted sum of a current signal sample plus a finite number ofpreviously sampled values of the signal. Thus, for an N state FIR filterthere are N samples including the current sample S_(n) and the N−1 priorsamples S_(n-1) . . . S_(n-N) of the signal. These samples are weightedby multiplication of the sample values with N filter coefficients havingweighting values (commonly referred to a filter coefficients) that canbe in general designated c₀ . . . c_(N). In this example, the n index isused to designate the current sample. Thus, the filter output in generalis given by:

${{{Filter}\mspace{14mu}{{Output}(n)}} = {\sum\limits_{i = 0}^{N}{c_{i}{S\left\lbrack {n - i} \right\rbrack}}}},$

where i is a counting integer.

Selection and installation of filter coefficients can be implemented ina number of ways including, but not limited to, computing a set ofsuitable filter coefficients, adaption of a set of filter coefficients,adding or removing filter sections, or selection of a set of filtercoefficients from a plurality of pre-defined and stored filtercoefficients. The latter approach is depicted in this example system 100with multiple sets of filter coefficients being stored in a filtercoefficient memory 164 that contains a table of filter coefficients fora range of filter characteristics ranging from a narrowest useful filterbandwidth through one or more intermediate filter bandwidths to a widestuseful filter bandwidth. Block 160 selects a set of filter coefficientsfrom memory 164 and loads the filter coefficients into the digitallow-pass channel filter 150.

So, for example, in one implementation three ranges of SNR can be usedto determine the filter coefficients of the channel filter 150 so as toutilize either a narrow, intermediate or wide bandwidth channel filter(as illustrated in FIG. 1-4). In this example, three sets of filtercoefficients C_(narrow), C_(intermediate) and C_(wide) can be used in anexample 24 stage FIR filter. The particular filter design is dependentupon the application as are the detected SNR thresholds as estimated,but in this example, the estimated SNR thresholds are set at SNR<10 db,10 db≦SNRdb≦ISNR, and 20 db<SNR for purposes of providing anillustrative example. The decision as to which filter coefficients areto be installed in channel filter 150 can be generally summarized in thefollowing table in which the filter coefficients are subject to designof the actual filters to achieve the desired characteristics of thenarrow, intermediate and wide filters for the particular application athand:

Example SNR SNR Filter Estimate Range Bandwidth Coefficient Set Low SNR< 10 dB Narrow C_(narrow0) . . . C_(narrow24) Inter- 10 db ≦ Inter-C_(intermediate0) . . . C_(intermediate24) mediate SNR ≦ 20 dB mediateHigh 20 db < SNR Wide C_(wide0) . . . C_(wide24)

While three sets of filter characteristics are depicted in this example,those skilled in the art will appreciate upon consideration of thepresent teachings that more or fewer sets of filter coefficients couldbe used. Moreover, other techniques for altering the bandwidth ofchannel filter 150 are also contemplated.

Referring back to FIG. 5, the decimated I and Q values from decimator144 are processed by any suitable digital FFT 172 (for example) todetermine which parts of the I and Q signals represent signal and whichparts represent noise. In one implementation, the ratio ofsignal-to-noise estimate is computed and used either as a raw number orafter conversion to decibels and that number is passed to the channelfilter control and decision logic block 160. Block 160 then takes thatnumber representing SNR and utilizes a table similar to that depictedabove to select either coefficient set C_(narrow), C_(intermediate) orC_(wide) and installs those filter coefficients into channel filter 150for use in the channel filtering operation carried out on the decimatedI and Q signals from 144.

Block 160 may be implemented as either a programmed processor or as adedicated hardware logic circuit or any combination thereof. Thesefilter coefficients may serve, for example, as weighting functions thatare distributed throughout the filter for weighting delayed versions ofthe input signal which are summed together to obtain the output signalin a known manner. In operation, the channel filter may start out with adefault (compromise) bandwidth determined by an initially loaded set offilter coefficients to operate in much the same way as a fixed filter.From there, the analysis described below is carried out to adjust andadapt the channel filter 150 to provide a more optimal filtering.

When the decimated I and Q signals are output by the decimator 144, theyare received as a filter input at channel filter 150 but are alsoexamined by a pre-filter SNR estimation circuit 168. This circuit, thatcan be either hard wired logic or implemented using a programmedprocessor, carries out an estimation of the decimated baseband I and Qsignal's signal-to-noise ratio. This can be carried out in any number ofways. For example, a Fast Fourier Transform (FFT) operation (which is aform of Digital Fourier Transform or DFT) depicted as 172 can be carriedout on the decimated baseband signal to produce a representation of thespectrum of the signal at the channel filter input. This representationof the spectrum can then be used to calculate an estimate of the SNR ofthe input signal to the channel filter 150. This estimate can be in theform of an actual SNR in dB, a ratio of voltages, a ratio of powers, orindividual values of signal and noise powers without limitation.Depending upon various circuit and application parameters, thispre-filtering estimate may be obtained quickly since the signal at thechannel filter input is not delayed by the channel filter 150 itself,which imposes a delay.

The signal-to-noise ratio can also be estimated (generally with greateraccuracy but slower) at the output of channel filter 150 by use of apost-filter SNR estimation block 176. This block can also utilize FFTanalysis on the filtered output of the channel filter 150 or can derivean estimate of SNR using any suitable mechanism. In one example,depicted by use of the dashed line from demodulator 154 to block 176, itis noted that many demodulator circuits 154 already provide forcomputation of signal-to-noise ratio for various purposes includingdisplay of signal quality and as a figure of merit for the receiver'sperformance, etc. In such cases, the SNR can be computed normally andfed to the control and decision block 160 for processing. Customprocessing of this signal at the channel filter 150 output may also beadvantageous in the event an optimal filter characteristic can beestimated. In any case, the SNR estimates can be utilized to determinewhich of a plurality of sets of filter coefficients can beadvantageously selected for use by the channel filter 150.

One example implementation of an operational process 200 is depicted inFIG. 6 starting at 202. After initialization and booting operations forthe radio 100 are completed, the analog portion of the radio receiverbegins supplying I/Q signals to the digital portion of the radioreceiver at 206. In this implementation, the digital portion of thereceiver begins estimating the SNR, for example at the I/Q signalsappearing at the input of the channel filter at 210. This can be done,for example, by use of a digital Fast Fourier Transform (FFT or DFT) orusing any other suitable method. In this case, using an FFT providesinformation about the spectrum frequencies of interest within thedesired channel as well as a region extending somewhat beyond thechannel, but which can affect the post-filtering SNR if the channelbandwidth is wider than normal.

In the current example, three sets of filter bandwidths corresponding tothe three sets of filter coefficients are used to establish the channelfilter bandwidth. They will be referred to herein as wide, intermediateand narrow as illustrated earlier in FIGS. 1-4. The actual numericalvalue of frequency bandwidth for each of these channel filter bandwidthis not essential to the understanding of the present implementation andit will be understood by those skilled in the art that the bandwidthwill be determined by the specific application of the radio receiver.However, for purposes of providing an illustrative example, the threepassband bandwidths for a Global System for Mobile communication (GSM)second generation (2G) radio receiver application may be approximately80 KHz (narrow), 100 KHz (intermediate) and 120 KHz (wide) as a startingpoint, but these bandwidths should only be considered as a startingpoint for experimentation in this particular radio application andshould not be considered limiting. Any number of two or more sets ofbandwidth ranges can be used in a manner consistent with the presentteachings. These channel filter characteristics are established byloading one of three corresponding sets of stored filter coefficientsinto the channel filter 150. The channel filter 150 may be initializedusing the intermediate bandwidth coefficients as an initialized startingpoint for filtering in certain implementations.

The SNR estimate taken at 210 includes both a post-filter SNR estimateof the SNR at the output of the channel filter 150 and a pre-filter SNRestimate at the input of the channel filter 150. This post-filterestimate of SNR is stored at 214 for later retrieval. The pre-filter SNRestimate is evaluated at 218 to determine if it is to be considered low,moderate or high for a particular application. Again, the determinationof what constitutes high, moderate or low SNR is application specific,and should be determined based on the particular application. Forpurposes of explanation, and as a reasonable starting point forexperimentation using the wide, intermediate and narrow bandwidths abovein a GSM 2G cellular telephone receiver, one could start out utilizingbelow 10 db (low), between 10 db and 20 db inclusive (intermediate) andgreater than 20 db (high) as the three threshold ranges for purposes ofdecision making in the channel filter control and decision logicfunction 160. It is understood that the above ranges are merelysuggested starting points that can be better refined by experimentationin a given receiver architecture and are not to be considered limitingin any manner. It is again noted that in other implementations, at leasttwo such ranges are used, but more than three ranges could be used asdesired. The filter characteristics in this example are determined bythree corresponding sets of filter coefficients to implement, forexample, a finite impulse response (FIR) or infinite impulse response(IIR) digital filter having bandwidth corresponding to the above threeexample filter bandwidths.

If upon evaluation of the pre-filtering SNR at 218, the SNR is in thelow range indicating low signal strength relative to noise orinterference or both, the channel control and decision logic 160 selectsand applies the narrow pass band bandwidth filter coefficients andinstalls them into channel filter 150 at 222. If upon evaluation of thepre-filtering SNR at 218, the SNR is in the moderate range indicatingmoderate signal strength relative to noise or interference or both, thechannel control and decision logic 160 selects and applies theintermediate pass band bandwidth filter coefficients and installs theminto channel filter 150 at 226. If upon evaluation of the pre-filteringSNR at 218, the SNR is in the high range indicating high signal strengthrelative to noise or interference or both, the channel control anddecision logic 160 selects and applies the wide pass band bandwidthfilter coefficients and installs them into channel filter 150 at 230. Ineach instance 222, 226 and 230, upon completion of installation of thecoefficients into the channel filter 150, control passes to 234 wherethe results of changing the filter coefficients are evaluated. This canbe done by a comparison of the post-channel filter SNR estimate storedat 214 with a newly estimated post channel-filter SNR done afterinstallation of the channel filter coefficients installed at 222, 226 or230.

If at 238, the newly estimated post-filtering SNR is greater than orequal to the previously stored post-filtering SNR stored at 214, thefilter change has been successful or at least not detrimental inimproving the SNR and the new filter settings are retained. If thepost-filtering SNR is less than the SNR stored at 214 then the filterchange has been detrimental and the filter control and logic process 160reverts the channel filter coefficients back to their prior setting at246. After 242 or 246, the process waits for a specified time (e.g., 10to 100 milliseconds, for purposes of an illustrative but non-limitingexample) at 250 and the process repeats starting at 210 so that thechanging environment of the radio receiver can be quickly compensatedfor by adjustment of the channel filter characteristics. In anotherexample, the pre-filter SNR can be continuously monitored and the entirefilter characteristic change process can be initiated in the event ofany substantial change in the pre-filter SNR estimation. Othervariations will occur to those skilled in the art upon consideration ofthe present teachings. It is to be noted that all numerical examplesgiven herein are to be considered examples without any intent to limitthe bounds of the present teachings.

Many variations of this process will occur to those skilled in the artupon consideration of the present teachings. For example, in certainimplementations, the pre-filter SNR estimate may be used to change thedefault channel filter coefficients as a quick estimate while thepost-filter SNR estimate can be utilized to fine tune the filtercoefficients to further refine the channel filter properties. In otherimplementations, the pre- and post-channel filter SNR estimates can beaveraged or otherwise combined to refine the estimate of SNR toestablish the filter coefficients. The pre-filter SNR estimate can alsobe utilized to quickly determine that conditions of the channel arechanging and to adapt the channel filter accordingly. In otherimplementations, only one or the other of the SNR estimates may beutilized. Other variations will also occur to those skilled in the artupon consideration of the present teachings.

In certain example implementations, once an estimate of SNR is produced,the channel filter control and decision logic maps the SNR estimate to aprescribed range of signal-to-noise ratios stored in memory withparticular SNR ranges having corresponding particular sets of filtercoefficients, as illustrated by the table above. This is described inthe form of an example set of ranges above. Once a comparison of the SNRwith the ranges is completed, the SNR can be mapped to its correspondingset of filter coefficients which can then be loaded into the channelfilter 150 in order to effect the change in bandwidth of the channelfilter 150. The process can be repeated at regular time intervals toperiodically refine the channel filter characteristics to changingconditions. Alternatively, changes in conditions can be detected bysignificant changes SNR or other signal characteristics and such changescan be used to trigger a change in the channel filter coefficients. As afurther alternative, the SNR estimation can be carried out on acontinuous basis with the channel filter coefficients being changedwhenever a comparison of the current SNR estimate is outside the boundsof the SNR range mapped to the current set of channel filtercoefficients. SNR need not be expressed in dB by the block 168 forspeed, and various rounding or integer math techniques can be utilizedto speed the calculation as desired. Other variations will occur tothose skilled in the art upon consideration of the present teachings.

In certain example implementations as depicted in FIG. 7 the digitalportion of radio 100 is shown in simplified form as system 300. In thisimplementation example, one or more programmable processors representedby processor 304 is utilized to carry out the functions of processingblocks 160, 168, 172 and 176 of radio 100. For ease of illustration, thedecimator 144, channel filter 150 and demodulator 154 are shown asseparate functional blocks, but these functions may also be carried outin whole or in part using processor 304 or using other processors orutilizing dedicated hardware circuits or any combination of the abovewithout limitation. The functional blocks are shown communicating usinga communication bus 308 which is symbolic of one or more communicationpaths that can be utilized. Multiple bus structures and directcommunication between certain of the functional blocks is contemplatedand represented in simplified form by communication bus 308.

The processor 304 is coupled to memory 312 made up of any one or moretypes of storage device technologies such as random access memory (RAM),read only memory (ROM), flash memory, etc. to store functional programblocks that carry out various digital radio functions as described. TheFFT program block 316 stores instructions that carry out the FFTfunction used in block 172. The channel filter control and decisionlogic block 160 is implemented using program instructions in block 320.The pre-filter SNR estimation function 168 and post-filter SNRestimation function 176 and associated SNR to filter coefficient mappingare carried out using program instructions stored in block 324. Thefilter coefficients and their mapping to SNR ranges are stored at 328.

Referring now to FIG. 8, a generalized process consistent with certainimplementations is provided as process 400. At 404 the RF signal isconverted to baseband, for example using a direct conversion process. Anestimate of the baseband SNR is generated at 408 using either a pre- orpost-channel filter I/Q signal representing the baseband signal to makethe estimate using any suitable process. This SNR estimate is comparedto a set of SNR thresholds (one or more thresholds or ranges of SNRvalues) at 412. In accord with this comparison, a set of filtercoefficients is selected at 416 for use in establishing the operationalparameters including bandwidth of the channel filter. At 420, suchoperational parameters are selected for the channel filter, for exampleby installation of filter coefficients or otherwise modification of theoperational attributes of the filter. Many variations are possiblewithout departing from this implementation.

Another example of a generalized process consistent with certainimplementations is depicted in FIG. 9 as process 500. At 502, thebaseband I/Q signals are received and a FFT is calculated at 506. Oncethe FFT is calculated, the SNR can be generated from the FFT byidentification of the part of the I/Q signals in the frequency domainthat constitute signals and determining the power of the signal portion.Everything else is considered noise from the perspective of SNR, so thesignal power can be subtracted from the total power or the non-signalpower can be separately calculated and the ratio of signal-to-noiseconstituting the estimated SNR can be calculated at 510. This SNRestimate is compared to prescribed threshold values at 514 and theresults are mapped to a set of filter coefficients at 518. Thecoefficients and SNR ranges can be stored, for example in a table ordatabase within memory 312 at 328. These filter coefficients can then beinstalled into the channel filter 150 at 522 to establish the filtercharacteristics including bandwidth at channel filter 150.

The processes 400 and 500 can be iterated or repeated on a periodicbasis to account for changes in the noise and interferencecharacteristics of the channel as a result of the continuously changingenvironment of use of radio 100.

While the blocks representing the methods are shown as occurring in aparticular order, it will be appreciated by those skilled in the artthat certain of the blocks may be rearranged and can occur in adifferent order than that shown without materially affecting the endresults of the methods.

The implementations of the present disclosure described above areintended to be examples only. Those of skill in the art can effectalterations, modifications and variations to the particular exampleembodiments herein without departing from the intended scope of thepresent disclosure. Moreover, selected features from one or more of theabove-described example embodiments can be combined to createalternative example embodiments not explicitly described herein. Thoseskilled in the art will appreciate, upon consideration of the presentteaching, that the processes described above, when used in a programmedprocessor implementation, can be implemented in any number of variationsand in many suitable programming languages without departing from thepresent teachings. For example, the order of certain operations carriedout can often be varied, additional operations can be added oroperations can be deleted without departing from certain embodiments ofthe teachings herein. Error trapping can be added and/or enhanced andvariations can be made i without departing from the teachings herein. Itwill be further appreciated that while examples based upon computerprograms installed in a processor are depicted, all elements of thedigital radio could equivalently be implemented using hardware statemachines without departing from the present teachings. Such variationsare contemplated and considered equivalent.

It will be appreciated that any module or component disclosed hereinthat executes instructions may include or otherwise have access tonon-transient and tangible computer readable media such as storagemedia, computer storage media, or data storage devices (removable ornon-removable) such as, for example, magnetic disks, optical disks, ortape data storage. The term “non-transient” is intended only to excludepropagating signals or waves and does not exclude volatile memory orrewritable memory devices. Computer storage media may include volatileand non-volatile, removable and non-removable media implemented in anymethod or technology for storage of information, such as computerreadable instructions, data structures, program modules, or other data.Examples of computer storage media include RAM, ROM, EEPROM, flashmemory or other memory technology, CD-ROM, digital versatile disks (DVD)or other optical storage, magnetic cassettes, magnetic tape, magneticdisk storage or other magnetic storage devices, or any other mediumwhich can be used to store the desired information and which can beaccessed by an application, module, or both. Any application or moduleherein described may be implemented using computer readable/executableinstructions that may be stored or otherwise held by such computerreadable media. Similarly, while the examples shown depict functionalblocks that may be implemented by installation of programming onto acomputer, the functional blocks can equivalently be implemented usinghard wired logic and the like without deviation for implementationsconsistent with embodiments of the present invention.

The present disclosure may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the disclosure is, therefore,indicated by the appended claims rather than by the foregoingdescription. All changes that come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. A device, comprising: a radio receiver circuitconfigured to receive a radio frequency signal and produce a basebandsignal as an output therefrom; a channel filter having a bandwidth, thechannel filter configured to receive the baseband output at a filterinput and produce a filtered output at a filter output thereof; asignal-to-noise ratio (SNR) estimator configured to estimate apre-filtering and post-filtering signal-to-noise ratio of the basebandsignal present at the channel filter input; and a filter controllerconfigured to receive the signal-to-noise ratio estimate and control thechannel filter to adjust the bandwidth thereof in accord with thesignal-to-noise ratio estimate.
 2. The device in accordance with claim1, where the SNR estimator further comprises: a pre-filteringsignal-to-noise ratio estimator that estimates the pre-filteringsignal-to-noise ratio present at the channel filter input; apost-filtering signal-to-noise ratio estimator that estimates thepost-filtering signal-to-noise ratio present at the channel filteroutput; and the filter controller configured to receive thepre-filtering SNR estimate and the post-filtering SNR estimate andcontrol the channel filter to adjust the bandwidth thereof in accordwith the pre- and post-filtering signal-to-noise ratio estimate.
 3. Thedevice in accordance with claim 1, where the SNR estimator furthercomprises: a pre-filtering signal-to-noise ratio estimator thatestimates the pre-filtering signal-to-noise ratio present at the channelfilter input; and the filter controller configured to receive thepre-filtering SNR estimate and control the channel filter to adjust thebandwidth thereof in accord with the pre-filtering signal-to-noise ratioestimate.
 4. The device in accordance with claim 3, where the SNR isestimated by calculating a Fast Fourier Transform (FFT) of a frequencyspectrum present at the channel filter input.
 5. The device inaccordance with claim 1, where the SNR estimator further comprises: apost-filtering signal-to-noise ratio estimator that estimates thepost-filtering signal-to-noise ratio present at the channel filteroutput; and the filter controller configured to receive thepost-filtering SNR estimate and control the channel filter to adjust thebandwidth thereof in accord with the post-filtering signal-to-noiseratio estimate.
 6. The device in accordance with claim 5, furthercomprising a demodulator where the SNR of the baseband signal isestimated at the channel filter output.
 7. The device in accordance withclaim 1, where the channel filter comprises a digital filter with thebandwidth of the channel filter selected by selection of a set ofchannel filter coefficients specified by the filter controller.
 8. Thedevice in accordance with claim 1, where the SNR estimate is mapped tothe set of channel filter coefficients by the filter controller.
 9. Thedevice in accordance with claim 1, where the filter controller isconfigured to compare a first SNR estimate at the output of the channelfilter prior to adjusting the bandwidth of the channel filter with asecond SNR estimate at the output of the channel filter after adjustingthe bandwidth of the channel filter; if the second SNR estimate isimproved over the first SNR estimate, then the adjusted channel filteris retained; and if the second SNR estimate degraded over the first SNRestimate, then the channel filter is readjusted to have thepre-adjustment bandwidth.
 10. The device in accordance with claim 1,where the baseband output comprises a baseband output from a decimator.11. The device in accordance with claim 1, where the radio receivercircuit comprises a direct conversion radio receiver.
 12. A method,comprising: at a radio receiver circuit, receiving a radio frequencysignal and producing a baseband signal as an output therefrom; at achannel filter having a variable bandwidth, receiving the basebandoutput at a filter input and producing a filtered output at a filteroutput thereof; estimating a pre-filtering and post-filteringsignal-to-noise ratio (SNR) of the baseband signal present at thechannel filter input; and controlling the channel filter bandwidth inaccord with the estimate of the SNR of the baseband signal.
 13. Themethod in accordance with claim 12, where estimating the SNR furthercomprises: estimating the pre-filtering signal-to-noise ratio present atthe channel filter input; estimating the post-filtering signal-to-noiseratio present at the channel filter output; and where the controllingcomprises receiving the pre-filtering SNR estimate and thepost-filtering SNR estimate and adjusting the bandwidth of the channelfilter therefrom.
 14. The method in accordance with claim 12, where theSNR estimating further comprises: estimating the pre-filteringsignal-to-noise ratio present at the channel filter input; and where thepre-filtering SNR estimate is used to adjust of the bandwidth of thechannel filter.
 15. The method in accordance with claim 14, where theSNR is estimated by calculating a Fast Fourier Transform (FFT) of afrequency spectrum present at the channel filter input.
 16. The methodin accordance with claim 12, where the SNR estimating further comprises:estimating the post-filtering signal-to-noise ratio present at thechannel filter output; and where the post-filtering SNR estimate is usedto adjust of the bandwidth of the channel filter.
 17. The method inaccordance with claim 16, further comprising estimating SNR at ademodulator receiving the channel filter output.
 18. The method inaccordance with claim 12, where the channel filter comprises a digitalfilter and further comprising selecting the bandwidth of the channelfilter by selection of a set of channel filter coefficients to controlthe channel filter bandwidth.
 19. The method in accordance with claim12, where the filter controller is configured to compare a first SNRestimate at the output of the channel filter prior to adjusting thebandwidth of the channel filter with a second SNR estimate at the outputof the channel filter after adjusting the bandwidth of the channelfilter; if the second SNR estimate is improved over the first SNRestimate, then the adjusted channel filter is retained; and if thesecond SNR estimate degraded over the first SNR estimate, then thechannel filter is readjusted to have the pre-adjustment bandwidth. 20.The method in accordance with claim 12, further comprising mapping theSNR estimate to a set of channel filter coefficients.
 21. The methodaccordance with claim 12, where the baseband output comprises adecimated baseband output.
 22. A method, comprising: at a radio receivercircuit, receiving a radio frequency signal and producing a basebandsignal as an output therefrom; at a digital channel filter having avariable bandwidth, receiving the baseband output at a filter input andproducing a filtered output at a filter output thereof; estimating apre-filtering signal-to-noise ratio present at the channel filter input;estimating a post-filtering signal-to-noise ratio present at the channelfilter output; and selecting a set of channel filter coefficients foruse by the channel filter that determine the channel filter bandwidth inaccord with the pre-filtering SNR estimate and the post-filtering SNRestimate of the baseband signal.
 23. The method in accordance with claim22, where at least one of the SNR estimates is made by calculating aFast Fourier Transform (FFT) of a frequency spectrum.
 24. Anon-transitory computer readable storage medium storing information thatwhen executed on one or more programmed processors carry out a process,comprising: receiving a baseband signal as an output from a radioreceiver; filtering the baseband signal at a channel filter having avariable bandwidth by receiving the baseband output at a filter inputand producing a filtered output at a filter output thereof; estimating apre-filtering and post-filtering signal-to-noise ratio (SNR) of thebaseband signal present at the channel filter input; and controlling thechannel filter bandwidth in accord with the estimate of the SNR of thebaseband signal.
 25. The storage medium in accordance with claim 24,where estimating the SNR comprises: estimating the pre-filteringsignal-to-noise ratio present at the channel filter input; estimatingthe post-filtering signal-to-noise ratio present at the channel filteroutput; and where the controlling comprises receiving the pre-filteringSNR estimate and the post-filtering SNR estimate and adjusting of thebandwidth of the channel filter therefrom.
 26. The storage medium inaccordance with claim 24, where at least one of the SNR estimates ismade by calculating a Fast Fourier Transform (FFT) of a frequencyspectrum.
 27. A device, comprising: a radio receiver circuit configuredto receive a radio frequency signal and produce a baseband signal as anoutput therefrom; channel filtering means having a bandwidth, thechannel filtering means for receiving the baseband output at a filterinput and producing a filtered output at a filter output thereof;signal-to-noise ratio (SNR) estimating means for estimating apre-filtering and post-filtering signal-to-noise ratio of the basebandsignal; and filter controlling means for receiving the signal-to-noiseratio estimate and controlling the channel filtering means to adjust thebandwidth thereof in accord with the signal-to-noise ratio estimate.